Abstract
We numerically investigate natural convection in a bottom-heated top-cooled cavity, fully and partially filled with adiabatic spheres (with diameter-to-cavity-size ratio d/L=0.2) arranged in a Simple Cubic Packing (SCP) configuration. We study the influence of packing height and location of porous media. We carry out the simulations using water as the working fluid with Prandtl number, Pr=5.4 at Rayleigh number Ra=1.16×105, 1.16 × 106 and 2.31 × 107. The applicability and suitability of Darcy-Forchheimer assumption to predict the global heat transfer is analysed by comparing it with the pore-structure resolved simulations. We found that the heat transfer in pore-structure resolved simulations is comparable to that in fluid-only cavities at high Rayleigh numbers, irrespective of the number of layers of packing and its location. Discrepancies in heat transfer between the Darcy-Forchheimer and the fully resolved simulations are observed when the porous medium is close to the isothermal wall and at high Ra, while it vanishes when the porous medium is away from the isothermal bottom wall.
Highlights
Natural convective heat transfer in porous media packed cavities is of great importance in various engineering and real-life applications
Discrepancies in heat transfer between the Darcy-Forchheimer and the fully resolved simulations are observed when the porous medium is close to the isothermal wall and at high Ra, while it vanishes when the porous medium is away from the isothermal bottom wall
At high Ra, the temperature and velocity of the thermal plumes impinging the hot wall are higher in the pore-structure resolved simulations resulting in heat transfer comparable to fluid-only cavities
Summary
Natural convective heat transfer in porous media packed cavities is of great importance in various engineering and real-life applications It is an important mechanism in refrigeration devices Laguerre et al (2008a,b), distribution transformers Torriano et al (2018), nuclear waste disposal Shams et al (2014), air dehumidifiers Fazilati et al (2016), catalytic reactors Li et al (2013); Thiagalingam et al (2015), etc. Studies report that the heat transfer in fully packed porous media filled cavities asymptotically approach the heat transfer in a fluid-only cavity at high Rayleigh numbers Keene and Goldstein (2015); AtaeiDadavi et al (2019a). We investigate the validity and applicability of the D-F assumption in partially filled cavities of different packing heights and locations, by comparing it with the pore-structure resolved simulations. We aim at providing an insight into the influence of local flow and thermal structures on the heat transfer in these cavities and explain the discrepancy in heat transfer between the pore-structure resolved and D-F simulations
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